THE COMPOSITION OF FLUORESCENT PSEUDOMONAD POPULATIONS ASSOCIATED WITH ROOTS IS INFLUENCED BY PLANT AND SOIL TYPE

Populations of fluorescent pseudomonads isolated from an uncultivated soil and from the roots of two plant species were previously shown to differ (P, Lemanceau, T, Corberand, L, Gardan, X, Latour, G, Laguerre, J,-M, Boeufgras, and C, Alabouvette, Appl, Environ, Microbiol, 61:100 4-1012, 1995), The diversities of fluorescent pseudomonads, from two u ncultivated soils and from the roots of two plant species cultivated i n these two soils, were compared, The phenotypic diversity of the bact erial isolates was characterized on the basis of biochemical and physi ological tests and on the basis of their ability to utilize 147 differ ent organic compounds, The genotypic diversity of the isolates was cha racterized on the basis of the types of 16S genes coding for rRNA (rDN A), their repetitive extragenic palindromic patterns by PCR, and plasm id profiles, Taxonomic identification of the isolates was achieved wit h both biochemical and physiological tests and by comparing their 16S rDNA types to those of reference and type strains of fluorescent Pseud omonas spp, Numerical analysis of phenotypic characteristics allowed t he clustering of isolates that showed high levels of similarity, This analysis indicated that both soil type and host plant had an effect on the diversity of fluorescent pseudomonads. However, of the two factor s studied, the soil was clearly the dominating one, Indeed, the popula tions associated with the roots of each plant species varied from one soil to the other, This variation could possibly be ascribed to the di fferences recorded between the phenotypically diverse populations of f luorescent pseudomonads from the two uncultivated soils, The plant sel ection was, at least partly, plant specific, It was not related to bac terial species and biovars or to the presence of plasmid DNA, The phen otypic clustering of isolates was well correlated with genotypic chara cterization by repetitive extragenic palindrome-PCR fingerprinting.